Main problems and solutions for natural gas vehicles

&nbsp; &nbsp;<span style=”font-weight: bold;”>Natural gas vehicles have obvious advantages in terms of emissions. Compared with gasoline-powered vehicles, natural gas vehicles have almost zero particulate emissions, and emit NOx, CO, and HC. It is also significantly reduced, so natural gas vehicles are of great significance in improving air quality. At the same time, natural gas vehicle technology has also undergone unprecedented development, from atmospheric natural gas vehicles in the past to compressed natural gas vehicles (CNG) and liquefied natural gas vehicles (LNG). Nevertheless, there are still some problems in the use of natural gas vehicles. Among them, the most prominent ones are the decline of engine power, engine corrosion and early wear.
1. Engine power drop and its reasons
(1) Automobiles use natural gas as fuel<br />&nbsp;&nbsp;&nbsp; A major problem in the use of natural gas vehicles is that the power of the engine is significantly lower than when gasoline is used. According to reports, when a car uses natural gas as fuel, the power is generally reduced by about 15%, and sometimes even more. As a result of the power drop, on the one hand, it causes insufficient power when the car is heavily loaded, climbing or accelerating; on the other hand, it leads to a relatively increase in fuel consumption and an increase in pollutant emissions.
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(2) The main reason for the power drop of natural gas vehicles is the characteristics of the fuel itself and the structure of the engine. <br />&nbsp;&nbsp;&nbsp; In terms of fuel nature, gasoline is a liquid fuel, while natural gas is a gas fuel. When gasoline is used, the volume of liquid gasoline is almost negligible compared to the intake air volume. However, when natural gas is used as fuel, the volume of the fuel itself occupies a large proportion of the entire intake air, which leads to a decrease in the amount of air entering the cylinder and the charge The coefficient drops, which leads to a drop in engine power.
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(3) In terms of engine structure, the main factor that determines engine power is the compression ratio of the engine. </strong></p><p><strong>The larger the compression ratio, the higher the thermal efficiency and the greater the effective power. At the same time, the greater the compression ratio, the greater the tendency of the engine to knock. Therefore, the engine compression ratio must also be compatible with the anti-knock properties of the fuel. The anti-knock property of gasoline determines that the compression ratio of gasoline engines cannot be too high, but the anti-knock property of natural gas is very good, and it can be used in engines with relatively large compression to increase its power. The application of natural gas vehicles is still in its infancy, and the supply of natural gas is far from being as popular as gasoline. In this case, specially designed natural gas engine vehicles have not yet been fully promoted. Many natural gas vehicles currently in operation are dual-fuel vehicles, which can use either natural gas or gasoline. In order to meet the needs of using gasoline, the compression ratio of this dual-fuel vehicle is small or not increased. Therefore, the high anti-knock properties of natural gas have not been fully utilized, resulting in a decrease in engine power.
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2. Corrosion and early wear and its causes Compared with gasoline, the car overhaul period is usually shortened by 1/3-1/2. This is another problem faced by natural gas vehicles. The reason for the corrosion and early wear of natural gas vehicles is that the natural gas contains trace sulfur compounds (hydrogen sulfide), which cause corrosion and wear of the cylinder and cylinder wall, which reduces the engine power, shortens the service life, and shortens the vehicle overhaul period.
3. Measures to increase the power of natural gas vehicles<br />(1) Increase the inflation coefficient<br />&nbsp;&nbsp;&nbsp; The decrease in the inflation coefficient is an important reason for the decrease in the power of natural gas vehicles. In theory, increasing the inflation coefficient is A way to increase power. However, the decrease in the inflation coefficient is determined by the nature of the natural gas itself. Obviously, this problem cannot be solved from the fuel aspect. The best solution is to take the intake air pressure boost. However, the intake supercharging will undoubtedly increase the volume and quality of the engine, and there are certain difficulties in implementation. <br />
(2) Appropriately increase engine compression ratio<br />&nbsp;&nbsp;&nbsp; Natural gas has a high octane number and excellent anti-knock properties. If natural gas is used directly on a gasoline engine, this advantage of natural gas cannot be fully utilized. Improve engine power. If the cylinder head of the engine is partly thinned and the compression ratio of the engine is increased, the power of the engine can be increased and part of the power loss can be compensated to a certain extent. This method is a method that people usually use. However, considering that most natural gas vehicles are currently dual-fuel vehicles, the engine compression ratio cannot be increased too much, otherwise, once the gasoline is used as fuel, knocking may occur. Therefore, the improvement of the compression ratio has a certain limit, which should be determined according to the actual situation. For example, when a car that originally used No. 70 gasoline is changed to a dual-fuel car, the compression ratio can be increased to that of a 90-number gasoline; when the original engine that uses No. 90 gasoline is changed to a dual-fuel car, the compression ratio can be changed. The ratio is increased to the compression ratio of using No. 93 or No. 95 gasoline. For cars that run on a fixed line like city buses and have a guaranteed supply of natural gas, the use of single-fuel natural gas cars with a compression ratio compatible with natural gas anti-knock resistance should be promoted to give full play to the characteristics of natural gas’s high compression ratio to improve the car’s engine. power.
(3) Use special natural gas automobile engine lubricating oil<br />&nbsp;&nbsp;&nbsp; Natural gas is a gas fuel, and there will be no engine lubricating oil dilution phenomenon in use, so lubricating oil with lower viscosity can be used, which can reduce viscosity The resulting power loss improves the efficiency of the engine. At the same time, the special engine lubricating oil for natural gas vehicles can effectively prevent the corrosion and wear of the combustion chamber components such as valves and piston rings, and prevent the power loss caused by the decrease of cylinder pressure. The natural gas engine lubricating oil and the ESC30 gasoline engine lubricating oil were used for comparative tests, the external characteristics and load characteristic curves. The fuel used in the test is all natural gas, and the fuel consumption is calculated based on the volume of natural gas under standard conditions. Compared with the use of ESC30 gasoline engine lubricating oil, the use of natural gas engine lubricating oil can increase the power and torque of the engine, and reduce the fuel consumption rate by about 10%.
<br />Four, measures to reduce corrosion and wear<br />
(1) Natural gas desulfurization<br />&nbsp;&nbsp;&nbsp; As mentioned earlier, the root cause of corrosion and early wear of natural gas vehicles is due to the trace amount of hydrogen sulfide contained in natural gas. Therefore, desulfurization of natural gas is an important means to reduce corrosion and wear. However, it is difficult to completely remove hydrogen sulfide when natural gas is desulfurized. Therefore, it is difficult to completely avoid the corrosion of natural gas to engines.
(2) The use of corrosion-resistant materials<br />&nbsp;&nbsp;&nbsp; The use of sulfide-resistant metal materials to manufacture engines is also an important measure to prevent corrosion. However, this method is only suitable for the manufacture of new engines and cannot do anything with existing engines. <br />
(3) Using special natural gas vehicle engine lubricating oil<br />&nbsp;&nbsp;&nbsp; Using natural gas vehicle engine lubricating oil instead of gasoline engine lubricating oil currently used is an effective measure to prevent natural gas vehicle engine corrosion. This method is not only simple, And it does not increase the cost. Compared with gasoline engine lubricating oil, natural gas vehicle engine lubricating oil has a higher alkali number and strong acid neutralization ability. The 50,000 km driving test shows that the natural gas special lubricating oil can effectively prevent hydrogen sulfide corrosion, reduce engine wear, and extend the engine overhaul period by more than 1/2. At present, some domestic lubricant manufacturers have conducted in-depth research on special lubricants for natural gas vehicles. For example, the special oil for CNG/gasoline dual-fuel engines developed and produced by Shaanxi General Petrochemical Co., Ltd. is aimed at a large number of oils on the market. The gasoline is converted to natural gas vehicles and developed and produced, and obtained national patent technology in 2006. Through the use of a large number of natural gas buses, taxis and other vehicles, good social and economic benefits have been achieved!

V. Conclusion 1. The reason for the decrease in the power of natural gas vehicles is due to the decrease of the inflation coefficient and the relatively low engine compression; 2. The reason for the early wear of the engine is caused by the trace sulfide in the natural gas; 3. Increase the power of the natural gas engine The main measures include air intake supercharging, increased engine compression ratio and use of special natural gas engine lubricating oil; 4. Ways to prevent corrosion and early wear include natural gas desulfurization, use of corrosion-resistant materials to make engines and use of special natural gas engine lubricating oil;</ strong></p><p><strong>5. The use of special natural gas engine lubricating oil has a significant effect on improving power and preventing engine corrosion and early wear. It is a simple, economical and effective measure. </strong></p>&nbsp;&nbsp;

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